The present invention relates generally to a rotary cutting device for the cutting of windows, notches, cavities, orifices or other patterns in relatively thin, flexible sheet-like material in either sheet or web form and, more particularly, to a clamping mechanism for retaining a cutting die adjacent to a die holder surface.
U.S. Pat. No. 4,823,659 to Falasconi having common ownership herewith describes one embodiment of a conventional rotary panel cutting apparatus for cutting windows, notches, cavities, orifices or other patterns in relatively thin, flexible sheet-like material typically found in either sheet or web form. The cutting apparatus may be used to produce envelopes having a transparent panel or window for allowing visual inspection of the enclosure. The window envelopes are manufactured from a web of material which is initially cut into blanks having a predetermined shape. A panel is subsequently cut from the blank to form the window. Thereafter, the blank is then folded, gummed, printed and packaged to form the finished envelope.
The cutting apparatus comprises a cutting tool in the form of a cutting plate or die and a rotary die holder which brings the cutting die into successive contact with the web and the blanks which advance on a conveyor system. The cutting die has a raised cutting edge which is adapted to engage the paper and cut a pattern such as the envelope sides or panels in the material. The die holder, sometimes called a die cylinder or drum, is mounted for rotation on a drive shaft synchronized with the conveyor system so that the cutting die engages a different blank for each rotation of the die holder.
Unfortunately, the prior art clamping mechanisms for holding a cutting die adjacent to the die holder surface suffer from numerous drawbacks. The typical clamping mechanism has at least one groove disposed around the periphery of the die holder for receiving a clamping key. The clamping key and the groove cooperate to clamp one of the cutting die ends therebetween for securing the cutting die to the holder. A second clamping key and groove may secure the other cutting die end. The cutting die must be retained adjacent the die holder surface, without any slack, to properly operate. The length of the cutting die typically must be manufactured within very strict tolerances, typically measured on the order of 0.001 inches in order to correctly align the cutting die, the clamping key and the groove. If the cutting dies are improperly manufactured, they will not fit. Cutting dies which are too short will not fit between the grooves whereas cutting dies which are too long will result in slack between the cutting die and the die holder surface instead of laying adjacent to the die holder surface resulting in inaccurate and improper cutting alignmenl Unfortunately, many conventional clamping mechanisms can not accommodate even slight variations in the cutting die dimensions. In addition, many clamping mechanisms secure the holding key to the groove using a plurality of screws which are expensive to manufacture and time consuming to assemble and disassemble. In some instances, the clamping action between the holding key and groove is insufficient to hold cutting die during the cutting operation so that the position of the cutting die may slip, resulting in improper and inaccurate cuts.
It is an object of the invention is to provide an improved cutting tool for cutting patterns in sheet-like material.
It is an object of the invention to provide a cutting tool having an improved clamping mechanism for holding the cutting die adjacent to the surface of the die holder.
It is a more specific object of the invention to provide an improved clamping mechanism which compensates for variations in the dimensions of the cutting die.
It is another object of the invention to provide a clamping mechanism which enhances the clamping force between the clamping bar and the die holder groove in order to secure retain the cutting die during the cutting operation.
It is an object of the invention to provide a die holder which functions in an efficient manner, is easily assembled and is adapted for operation with different size cutting dies.
It is a related object of the invention to provide a clamping mechanism which may be easily and readily adjusted to position the cutting die. In accordance with one aspect of the invention, a novel clamping assembly is provided for adjustably retaining the cutting die adjacent to the die holder. The clamping mechanism cooperates with a groove in the die holder for receiving at least one of the ends of the cutting die therebetween for securing the cutting die to the holder. In one embodiment, the clamping mechanism comprises a clamping bar and a position adjustment assembly for adjusting the vertical position of the clamping bar in the groove so as to accommodate different size cutting dies. The clamping mechanism comprises a biasing member disposed between the clamping bar and the groove for resiliently forcing the clamping bar outwardly and a retaining member for forcing the clamping bar inwardly. Once the clamping bar receives the end of the cutting die, the vertical position of the clamping bar in the groove may be adjusted to insure that the cutting die is properly seated on the die holder surface and that there is no slack between the cutting die and the die holder surface.
In another embodiment, the clamping mechanism comprises a clamping bar having a free end and a pivot end pivotably connected to the die holder so that clamping bar may pivotably enter the slot in the die holder. The clamping mechanism has one or more retaining members for retaining the free end after the clamping bar engages the slot. In yet another embodiment, the present invention provides a two-piece clamping bar with a pivot on each end and the retaining free ends are clamped at the center of the die holder longitudinal face. These and other features and advantages of the invention will be more readily apparent upon reading the following description of a preferred exemplified embodiment of the invention and upon reference to the accompanying drawings wherein: